Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art s widely known or forms part of the common general knowledge in the field.
In many industrial processes it is necessary to classify particles according to their size, and sometimes according to their density. For example, in mineral processing, screens, cyclones, and elutriators are often used to sort particles prior to downstream beneficiation. Classification may proceed either in a wet or a dry state. Although the aim may be to separate the particles at two specific sizes, there is usually a high degree of so-called misplaced material, with a portion of coarse particles reporting with the fine particle stream.
U.S. Pat. Nos. 6,814,241, 7,334,689, WO 2008/064406, and US 2014/0216986 disclose a device for separating particles by size or density using a fluidized bed in a chamber. In a preferred embodiment, the device separates low density particles from a feed slurry. The slurry is introduced below a set of substantially parallel inclined channels where the slurry is then fluidized by a fluidization fluid. The densest and largest particles located in the slurry settle to the bottom of the chamber and are removed through an underflow outlet. The remaining particles in the slurry are carried by a flow of fluidization fluid upward and into the inclined channels. Within the inclined channels, the flow carries the remaining particles upwards towards an overflow launder while simultaneously the particles settle towards a lower inclined surface of the inclined channels. The less dense and smaller particles then escape the device by passing out of the inclined channels and into the overflow launder before they are able to settle onto the lower surfaces of the inclined channels. The denser and larger particles return to the chamber, settling onto the lower surfaces of the inclined channels and then sliding down the lower surfaces and into the chamber. By this means, the low density particles report to the overflow and the high density particles are returned to the chamber and in turn report to the underflow. An example of a classifier with an array of parallel plates forming inclined channels is a Reflux™ classifier.
It has been found that in continuous operation material tends to build up within the inclined channels, which requires the device to be shut down for a period of time and cleaned by hand. These periods of shut down are costly, not only from the standpoint of labor to clean the device, but also from lost production due to machine being out of operation. In addition, it has been discovered that additional cleaning benefits can be realized and the performance of the classifier can be optimized by periodically injecting additional fluid, preferably water, into an area of the classifier located below an array of plates. In one embodiment, the thus injected water combines with the fluidization fluid and the liquid portion of the feed slurry while the device is in operation to thereby affect the movement of the particles through the inclined channels.
The present invention aims to provide a method or apparatus that can achieve the dual function of both cleaning the classifier device while optimizing its performance. The method and apparatus of the invention is utilized to prevent the buildup within the inclined channels and/or clean the inclined channels while the device is in operation eliminating the need for frequent shutdowns to clean the device. In addition, the apparatus is utilized to optimize the fluid flow through each array of inclined plates thereby improving the material separation. The apparatus of the invention is adapted to adjust the fluid flow through such array of inclined plates while the device is in operation depending on where a particular array of plates is located in the device and the distance of such array from the fluidized bed.